A technique to perform radiation therapy uses a radiotherapy device to target a radiation treatment beam onto a target volume (e.g., a tumor) of a patient. Such, radiation treatment beams emulate from a treatment radiation source, such as a megavoltage x-ray source. Here, the primary purpose of the x-ray source is to provide a sufficient dose of radiation to treat the target volume. Additionally such a radiotherapy device may include a separate imaging device used to image anatomy in the region of the target volume. This imaging device may use an imaging radiation source, such as a kilovoltage x-ray source. A radiation imager or detector is also used to capture the radiation after it passes through the patient. Information obtained from this imager can be used to adjust or verify correct positioning of patient anatomy and particularly of the target volume relative to the treatment beam.
The imaging device including an x-ray source and imager may be attached to a gantry that houses the treatment radiation source. One such design is typically embedded in a wall in a treatment area. In another design, the x-ray source and imager are attached inside a large diameter bearing (e.g., a cylinder) that the patient must enter for treatment.
With these gantry designs the movement of the x-ray source and the imager are limited to the movement of the gantry. That is, the arms that attach the x-ray source and the imager to the gantry are rigidly attached (e.g., stationary) or have limited ability to move in relation to the gantry. Furthermore, they have limited ability to be moved or stored “out of the way” to allow a technician unrestricted access to the patient, especially if the patient is being treated inside the bearing housing the x-ray source and imager. In addition, the inflexible manner in which the x-ray source and imager are attached to the gantry limits the movement of these treatment components independent from the movement of the gantry. For example, when the gantry is rotated to a specific position both components move with it, and the limited positions in which these components can be placed puts constraints on system movement and patient accessibility. Therefore, these designs limit the versatility of positioning an imaging beam and possibly even a treatment beam.
Another major disadvantage of such a system is the unintended consequence of mechanical flexure of the device. That is, the sagging weight of the x-ray source and/or imager may cause a misalignment of the imaging beam relative to the treatment beam. Such misalignment may result in unintended error in placing the target volume within the treatment beam thereby causing unintentional damage to healthy tissue and/or an inadequate dose delivered to the target volume during treatment. The proper targeting of the x-ray source to the treatment area is essential to delivery of the proper dose of radiation to the target volume and to minimize the dose of radiation to healthy tissue. Conventional radiotherapy devices do not have the capability to identify mechanical flexure in real-time and make corrections before administrating the treatment beam.